Field of the Invention
The present disclosure relates to an amorphous alloy, a molding die using the amorphous alloy, used for forming molded articles such as camera lenses, and a method for forming an optical element using the molding die.
Description of the Related Art
Press molding of glass material, which can be performed in a simple process without requiring cutting or polishing operation, can be applied to a process for forming optical elements. Accordingly, optical lenses, prisms and other optical elements have come to be formed by press molding.
The material of molding dies used for press molding of glass optical elements is required to have heat resistance, corrosion resistance, hardness, and releasability.
Many molding dies have been devised. For example, U.S. Pat. No. 4,629,487 discloses a molding die or mold formed in a desired shape of a cemented carbide that is hard and resistant to heat and oxidation, and coated with a releasing film of a chemically stable noble metal capable of releasing glass material therefrom.
On the other hand, various types of glass material have come to be used for a variety of optical designs. Some of the glass materials contain a reactive component, such as phosphorus or fluorine. For molding such a glass material, it is desirable the die have a releasing film unreactive with corrosive components released from the glass material. U.S. Patent Laid-Open No. 2009-0236494 discloses a molding die using a corrosion-resistant amorphous alloy for molding glass.
This corrosion-resistant amorphous alloy is chemically stable, but is not hard because it is intended for a layer to be cut. The present inventors measured some alloys expected to have high hardness selected from the amorphous alloys disclosed in U.S. Patent Laid-Open No. 2009-0236494. The hardest amorphous alloy of them had the composition of 58 atomic % of Pt, 21 atomic % of Hf, 12 atomic % of Zr, and 10 atomic % of Ni, and the hardness of this amorphous alloy was 9 GPa.
In the process of molding glass, super-hard powder is produced from super-hard members used in the molding die or the molding apparatus by rubbing of the super-hard members at a sliding portion. The hardness of super-hard members used in molding dies is generally about 13 GPa to 18 GPa. If glass is molded with a molding die on which super-hard powder from a sliding portion is deposited, the super-hard powder will be strongly pressed on the molding die by glass material. At this time, if the die is coated with a film having a hardness of about 9 GPa as the releasing film disclosed in U.S. Patent Laid-Open No. 2009-0236494 has, the coating film can be damaged or scratched by the super-hard powder. If glass optical elements are formed with such a damaged molding die, the scratches in the molding die are transferred to the glass optical elements, thus resulting in poor appearance of the glass optical elements.